make "require subscription" toggleable in build (#6144)

## Summary

Adds build time feature flags system starting with a flag that indicates
whether subscription is required to use the app. This is only used on
cloud.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6144-make-require-subscription-toggleable-in-build-2916d73d3650813bb140c5e96bcce1ce)
by [Unito](https://www.unito.io)

src/extensions/core/index.ts

@@ -26,5 +26,8 @@ import './widgetInputs'
 
 if (isCloud) {
   import('./cloudBadge')
-  import('./cloudSubscription')
+
+  if (__BUILD_FLAGS__.REQUIRE_SUBSCRIPTION) {
+    import('./cloudSubscription')
+  }
 }